This application claims the priority of German patent document DE 10 2005 007 159.7, filed Feb. 16, 2005, the disclosure of which is expressly incorporated by reference herein.
The invention is directed to a procedure for operating a high frequency amplifier.
German patent document DE 29 04 011 discloses a high frequency amplifier with a power transistor-amplifier stage (FIG. 1). On the emitter side an input interface network E receives an input signal RF_IN produced in a signal source SQ, and on the collector side an output interface network A supplies an output signal RF_OUT. In addition, on the emitter side a constant current source controlled from a pulse generator PG is connected to the amplifier stage VS, which impresses on the collector-emitter section of the power transistor LT of the amplifier stage VS a current corresponding to the pulse course for the duration of the pulse. In this manner, an adjustment of the transmission power and a modulation of the HF envelope are possible. On the collector side an operating voltage direct current lead BZ is provided for the power transistor LT.
One disadvantage of the circuit in German patent document DE 29 04 011 is that it is usable only for bipolar transistors in the basic circuit. Moreover the direct current source K in principle entails a large power loss.
FIG. 2 shows a circuit arrangement of a linear amplifier with a MOSFET power transistor LT. An input interface network E on the gate side is led to an input signal RF_IN produced in a signal source SQ, and an output interface network A on the drain side supplies an output signal RF_OUT. Further, on the gate side a voltage generator UG adjusts the operating point of the power transistor LT. A current source BZ is connected on the drain side of the power transistor.
A disadvantage of this circuit arrangement is the large power loss in transmission breaks or in low power transmission. An additional disadvantage is the thermal dependency of the amplification; that is, a temperature change of the power amplifier causes a corresponding change in the output power. Moreover there is a threshold voltage drift caused by change in the components.
A further disadvantage is the inaccurate transmission power adjustment in the dynamic operation of the transmission circuit.
German patent document DE 196 04 239 A1 discloses a high frequency amplifier in which the output power is held constant, although the supply voltage of a battery in the course of operation is smaller.
One object of the invention is to process for operating a high frequency amplifier with decreased power loss and temperature dependency, at more precise transmission power adjustment.
Another object of the invention is to provide such a process in which the HF envelope curve can be modulated.
These and other objects and advantages are achieved by the process according to the invention in which a high frequency amplifier includes a power transistor-amplifier stage in a source or transmitter circuit, for the amplification of the respective gate or base side high frequency signal supplied over an input interface network that is driven in such a way that the high frequency signals supplied over the input interface network amplified on the drain or collector side are taken over an output interface network. A device for the measurement of the drain or collector current I_D is connected at the amplifier stage on the drain or collector side, and on the gate or base side there is a variable attenuator to which a pre-settable desired value W_SOLL and an actual value W_IST corresponding to the drain or collector current is conducted. The gate voltage or the base current is adjusted over the variable attenuator in such a way that the drain or collector current I_D is subsequently led to the desired value W_SOLL, so that a constant input power P_IN of the high frequency amplifier modulates the envelope curve of the output signal RF_OUT by the desired value W_SOLL.
The procedure according to the invention is suitable for high frequency amplifiers with FET transistors as well as for high frequency amplifiers with bipolar transistors. In the following description, the designations drain, gate, or source side refer to FET transistors, while the designations collector, base, or emitter side refer to the bipolar transistors.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.